基金This work is supported by the Singapore National Research Foundation NRF RF Award No. NRFRF2010- 07, MOE Tier 2 MOE2012-T2-2-049, A'Star SERC PSF grant No. 1321202101, and MOE Tier 1 MOE2013- T1-2-235. W. Huang acknowledges the support of the National Basic Research Program of China (973 Program) (No. 2015CB932200), the National Natural Science Foundation of China (NSFC) (Grant Nos. 21144004, 20974046, 21101095, 21003076, 20774043, 51173081, 50428303, 61136003, and 50428303), the Ministry of Education of China (No. IRT1148), the NSF of Jiangsu Province (Grant Nos. SBK201122680, 11KJB510017, BK2008053, 11KJB510017, BK2009025, 10KJB510013, and BZ2010043), and NUPT (Nos. NY210030 and NY211022). J. R Wang is grateful for the NSFC (No. 11474164), NSF of Jiangsu province (No. BK20131413), and the Jiangsu Specially-Appointed Professor program. Y. L. Wang thanks Luqing Wang, Dr. Xiaolong Zou, and Dr. Alex Kutana for the constructive discussion.